The present invention relates to a damping assembly, and more particularly to a lightweight member, which is mountable to an airframe subcomponent to provide simultaneous localized structural stiffening and damping to reduce aircraft interior noise levels.
A primary determinant of aircraft interior noise levels is the response of the airframe structure to vibration excitation. Each individual component or subcomponent of an airframe has characteristic natural or resonant frequencies that can be coincident with one or more excitation frequencies. This would cause an individual component or sub-component to resonate and emit high noise levels, effectively acting as a speaker in the airframe.
Conventional constrained or shear layer damping has long been provided to address resonant response in an airframe, but damping treatments can be unacceptably heavy or have only limited effectiveness for thicker structural members such as helicopter transmission support beams. Modifying the stiffness of an individual component or subcomponent can also be effective in reducing noise by moving resonance frequencies away from excitation frequencies, but such modifications may require unacceptable design, structural analysis, certification and/or tooling costs for existing airframe designs.
Because resonance frequencies vary from airframe to airframe for a given aircraft model, adding stiffness by itself to an airframe component can adversely result in moving a given resonance frequency closer to an excitation frequency. A device that simultaneously adds both stiffening and damping, however, can potentially mitigate the shortcomings of both in certain applications.
Accordingly, it is desirable to provide a lightweight structural stiffening and damping assembly for airframe components, which does not impede inspection requirements or add additional resonance effects.